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Old 22nd February 2012, 12:30 AM   #461
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0.05C/W insted of 0.027 to keep the sinks at 25C above ambient.
900 x 0.05 = is 45C above ambient. with 900W of heat in a "smal" room. ambient is 30C+ you can allmost coffee on the sinks

Last edited by AudioSan; 22nd February 2012 at 12:37 AM.
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Old 22nd February 2012, 12:37 AM   #462
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Actually, i've measured the heatsink model of the KSA200(B), rather admired Krell for it at the time.
The later heatsink model that Krell had made, on e.g. KSA250 and MDA500, was even better. (me been very much into heatsinks since the '80s)
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Old 22nd February 2012, 12:39 AM   #463
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what was the numbers?
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Old 22nd February 2012, 12:44 AM   #464
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by jacco vermeulen View Post
0.325A bias per Motorola, 77Vdc rails, makes 25W.
Six on each heatsink, 36 total, makes 900W dissipation.

The heatsinks Krell used on the 200B are 0.30C/W, so they ran stupidly hot.
Why they broke down so often.

Now back to our regular scheduled program.
+10 Stove hot .....


Quote:
Originally Posted by jacco vermeulen View Post
Actually, i've measured the heatsink model of the KSA200(B), rather admired Krell for it at the time.
The later heatsink model that Krell had made, on e.g. KSA250 and MDA500, was even better. (me been very much into heatsinks since the '80s)
OK Mr heatsinks ....
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Old 22nd February 2012, 12:51 AM   #465
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Quote:
Originally Posted by AudioSan View Post
what was the numbers?
About 10% lower.

The 77Vdc is just a quicky from the memory bank, unloaded rail voltage, so think more like 850W dissipation.
Heatsink temperature was well above 65C in a hot room though, burnt your fingers. One had to dress light to audit a Krell display in those days.
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Old 22nd February 2012, 12:52 AM   #466
a.wayne is offline a.wayne  United States
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Are you talking about an KSA200 , it draws 1200-1400 watts at idle ....
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Old 22nd February 2012, 12:57 AM   #467
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Quote:
Originally Posted by jacco vermeulen View Post
About 10% lower.

The 77Vdc is just a quicky from the memory bank, unloaded rail voltage, so think more like 850W dissipation.
Heatsink temperature was well above 65C in a hot room though, burnt your fingers. One had to dress light to audit a Krell display in those days.
okei. thats about same as my numbers, when you withdraw the 50ish W.
guess ambient vas a little lower den 30C too
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Old 22nd February 2012, 01:07 AM   #468
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Sorry guys but can we keep this about the f5t boards?
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Old 22nd February 2012, 01:10 AM   #469
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yes we can
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Old 22nd February 2012, 01:12 AM   #470
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Quote:
Originally Posted by a.wayne View Post
at idle
From the wall socket maybe.
Doesn't mean that the heatsinks dissipate 1200 to 1400 watts.

For the record : 0.325A times 18 output devices per channel is 5.85A, divided by 2 makes a quiescent current setting of 2.925A. (the 325mV bias setting number is from the SM)
Is roughly 135 watts full class A (270 peak Class A), the KSA200 did way more than 300W in Class AB.

Most Class A power amps then, and still now, were biased to the peak power level.
Meaning that a power amplifier that was marketed as 100W Class A, was biased to 1.8A, which is 50W continuous and 100W peak Class A.
Everyone did that, saves 30% dissipation.

Now back to F5V, right ?
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